Sealed isocyanates

ABSTRACT

The present disclosure relates to sealed isocyanate resin compositions. The resin compositions may be used for additive manufacturing. One embodiment of the invention includes a photopolymerizable resin for additive manufacturing, the resin comprising: a blocked isocyanate; at least one monomer or oligomer; and a multifunctional nucleophile.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/660,894, filed Apr. 20, 2018, the contents of which are incorporatedherein by reference.

FIELD OF INVENTION

This invention is related generally to the field of additivemanufacturing, and more particularly to three-dimensional (3D) printingmaterials, methods, and articles made therefrom.

BACKGROUND

This application discloses sealed isocyanate compositions. Thecompositions described herein can be used with any of the embodimentsdiscussed, described, shown or claimed in U.S. Provisional PatentApplication No. 62/649,130 (“'130 application”) or in PCT internationalApplication No. PCT/US2019/24704. The full disclosures of theseapplications are incorporated herein by reference.

Many polymeric thermoplastic materials are high molecular weight,semi-crystalline polymers. These materials are 3D printable by additivemanufacturing techniques such as Fused Filament Fabrication (FFF) andSelective Laser Sintering (SLS). However, resin-based techniques (suchas Digital Light Projection (DLP), Stereolithography (SL) and polymerjetting) have been limited in their ability to produce these materialsdue to the constraints of the printing process.

Additive manufacturing or 3D printing refers to the process offabricating 3D objects by selectively depositing material layer-by-layerunder computer control. One category of additive manufacturing processesis vat photopolymerization in which 3D objects are fabricated fromliquid photopolymerizable resins by sequentially applying andselectively curing a liquid photopolymerizable resin using light, forexample ultraviolet, visible or infrared radiation. In some cases,thiol-ene resins may be used in these 3D printing processes.

Thiol-ene resins polymerize by reaction between mercapto compounds (—SH,“thiol”) with a C═C double bond, often from a (meth-) acrylate, vinyl,allyl or norbornene functional group, of the “ene” compound. For photo-initiated thiol-ene systems, the reaction follows a radical addition ofthiyl-radical to an electron rich or electron poor double bond. Thenature of the double bond may contribute to the speed of the reaction.The reaction steps of the radical-initiated, chain-transfer, step-growththiol-ene polymerization may proceed as follows: a thiyl radical isformed through the abstraction of a hydrogen radical; the thiyl radicalreacts with a double bond, cleaving it, and forms a radical intermediateof the β-carbon of the “ene”; this carbon radical then abstracts aproton radical from an adjacent thiol, through a chain transfer,reinitiating the reaction which propagates until all reactants areconsumed or trapped. In the case of di- and polyfunctional thiols andones, a polymer chain or polymer network is formed via radical stepgrowth mechanisms. Thiol-ene polymerizations can react either by aradical transfer from a photoinitiator or by direct spontaneous triggerwith UV-irradiation (nucleophilic Michael additions are also possiblebetween un-stabilized thiols and reactive ones).

In some cases, challenges may be encountered in the development ofthermoplastic-like materials in resin-based 3D printing technologies:crosslink density and crystallinity. One problem that may be encounteredis that not all resins have a high crosslink density. Resin based 3Dprinting techniques operate by causing a resin to gel and then fullycure (harden) by the exposure of the resin to light and sometimes theapplication of heat in a post baking step. To form a gel, the resin mustbecome sufficiently viscous through increases in molecular weight. Thisgelation requires a minimum amount of crosslinks (chemical or physical)to be formed between neighboring polymer chains. The larger the numberof crosslinks, the faster gelation occurs; the lower the number ofcrosslinks, the slower gelation occurs. Thus, for rapidly curingmaterials, a high number of crosslinks per molecule may be desired.

The relationship of crosslink density to speed of gelation is inverselyproportional to the elongation of the material. To maximize elongation,lower crosslink density is desired, enabling longer segments of polymerchain to unravel as the polymer is stressed, which can lead to greaterelongation before failure. Thus, a tradeoff may be made between printingspeed and the ultimate elongation of the material. A 3D printable resinwhich is able to be printed with high crosslink density and, afterprinting, can have crosslinks selectively cleaved to enable lowercrosslink density, and thus higher elongation, may be valuable.

Another problem that may be encountered is that some resins may notproduce thermoplastic polymers with the desired amount of crystallinity.Crystallinity enables thermoplastic polymers to be tough, providingtransient, physical crosslinks which can break and reform to dissipateenergy. Crystalline materials may be difficult to 3D print viaresin-based techniques. This may be because most crystalline materialshave high melt transition temperatures (>100° C. often from π-stackingor hydrogen bonding) and require high temperatures to melt, or solventsto dissolve, them. Both of these aspects may be problematic, as somesolvents may interfere with the 3D printing process, especially withdimensional stability and fidelity, and high heat may cause the reactionto prematurely gel because the photoinitiator in the system may act as athermal initiator at elevated temperatures). Low melting crystals (<100°C. often long chain aliphatic hydrocarbon, ester or ether chains) areoften waxy, having poor overall properties and chain slippage at lowtemperatures. It may be beneficial to obtain a polymer which, whenprinted is amorphous, however, after printing to the polymer becomescrystalline with a high melt temperature.

There remains a need for improved three-dimensional (3D) printing resinmaterials to overcome any of the problems noted above. The disclosedembodiments may address ore or more challenges associated with othermaterials systems.

SUMMARY

The present disclosure relates to sealed isocyanate photopolymerizableresin compositions. The resin compositions may be used for additivemanufacturing.

One embodiment of the invention includes a photopolymerizable resin foradditive manufacturing, the resin comprising: a blocked isocyanate; atleast one monomer or oligomer; and a multifunctional nucleophile.

Another embodiment includes a powder composition for additivemanufacturing, the powder comprising: a powdered blocked isocyanate, anda powdered dial.

Another embodiment includes a photopolymerizable resin for additivemanufacturing in an oxygen environment, the resin comprising: a blockedisocyanate; a crosslinking component; at least one monomer or oligomer;and a chain transfer agent comprising at least one of a thiol, asecondary alcohol, or a tertiary amine, wherein the resin is configuredto react by exposure to light to form a cured material, wherein thechain transfer agent is configured to permit at least some bondingbetween a layer of resin previously cured and an adjacent, subsequentlycured layer of resin, despite an oxygen-rich surface present on thepreviously cured layer of resin at an interface between the previouslycured layer of resin and the subsequently cured layer of resin.

Another embodiment includes a photopolymerizable resin for additivemanufacturing printing in an oxygen environment, the resin comprising: ablocked isocyanate a photoinitiator, wherein the photoinitiator isconfigured to generate a free radical after exposure to light; acrosslinking component; and at least one monomer or oligomer, whereinthe crosslinking component and the at least one monomer or oligomer areconfigured to react with the free radical to provide growth of at leastone polymer chain radical within a volume of the photopolymerizableresin, wherein the at least one polymer chain radical reacts withdiffused oxygen to provide an oxygen radical; and a chain transfer agentcomprising at least one of a thiol, a secondary alcohol, or a tertiaryamine, wherein the chain transfer agent is configured to transfer theoxygen radical to initiate growth of at least one new polymer chainradical.

Another embodiment includes a photopolymerizable resin, the resincomprising: a blocked isocyanate; a crosslinking component; at least onemonomer or oligomer, wherein the crosslinking component and the at leastone monomer or oligomer are configured to react to provide one or morepolymer chains after exposure to light; and a chain transfer agentcomprising at least one of a thiol, a secondary alcohol, or a tertiaryamine, wherein the chain transfer agent is configured to transfer a freeradical associated with the one of the polymer chains to another one ofthe polymer chains.

Another embodiment includes a storage-stable photopolymerizable resinmixture, the resin mixture comprising: at least one monomer or oligomer;and a blocked isocyanate, wherein the blocked isocyanate is configuredto liberate the reactive isocyanate functionality; wherein aftercombination of the components, the resin mixture exhibits no more than100% increase in the viscosity after 1 week at room temperature.

Another embodiment includes a photopolymerizable resin for additivemanufacturing, the resin comprising: a blocked isocyanate; acrosslinking component; at least one monomer or oligomer; aphotoinitiator, wherein the photoinitiator is configured to generate afree radical after exposure to light wherein the free radical initiatesa chain reaction between the crosslinking component and the at least onemonomer or oligomer to provide one or more polymer chains within avolume of the photopolymerizable resin; a chain transfer agentcomprising at least one of a thiol, a secondary alcohol, or a tertiaryamine, wherein the chain transfer agent is configured to reinitiate thechain reaction to provide one or more new polymer chains within a volumeof the photopolymerizable resin, wherein a layer of the resin about 100μm thick is configured to form a cured material in no more than 30seconds; wherein the resin has a viscosity at room temperature of lessthan 1,000 centipoise.

Another embodiment includes a photopolymerizable resin for additivemanufacturing, the resin comprising: a blocked isocyanate; less than 5%of a thiol; at least about 50% of one or more monomers; and aphotoinitiator, wherein the photoinitiator is configured to form a freeradical after exposure to light, such that the free radical initiatesgrowth of one or more polymer chains including at least the difunctionaland monofunctional monomers; wherein the thiol is configured to promotecontinued growth of the one or more polymer chains, wherein the resin isconfigured to react by exposure to light to form a cured material,wherein the cured material has a glass transition temperature in therange about 5-30° C.

Another embodiments includes a photopolymerizable resin for additivemanufacturing, the resin comprising: a blocked isocyanate; less thanabout 5% of a thiol; and at least about 50% of one or more monomers;wherein the resin is configured to react to form a cured material;wherein the cured material has a toughness in the range about 3-30 MJ/m³and a strain at break ranging in the range about 30-300%.

Another embodiment includes a photopolymerizable resin for additivemanufacturing, the resin comprising: a blocked isocyanate; less thanabout 5% of a thiol; and at least about 60% of one or more monomers,wherein the resin is configured to react by exposure to light to form acured material; wherein the cured material has a toughness in the rangeabout 3-100 MJ/m³ and a strain at break in the range about 200-1000%.

Another embodiment includes a photopolymerizable resin for additivemanufacturing, the resin comprising: a blocked isocyanate; at least atleast one monomer or oligomer; and less than about 20% of a thiol,wherein the resin is configured to react by exposure to light to providea cured material, wherein the cured material produces less than 1 partper 100 million of thiol volatiles at ambient temperature and pressureover 50 seconds in an oxygen environment.

Another embodiment includes a photopolymerizable resin for additivemanufacturing, the resin comprising: a blocked isocyanate; less thanabout 5% of a thiol; at least about 50% of one or more acrylic monomers;and less than about 45% of one or more acrylic-functionalized oligomers,wherein the resin is configured to react by exposure to light to form acured material; wherein the resin has a viscosity at room temperature ofless than 1,000 cP; wherein the components of the resin can be combinedand stored in a single pot for at least 6 months at room temperaturewith no more than 100% increase in the viscosity of the resin.

Another embodiment includes a photopolymerizable resin for additivemanufacturing, the resin comprising: a blocked isocyanate; less thanabout 5% of a stabilized thiol; at least 50% of one or more acrylicmonomers; and less than about 45% of one or more acrylic-functionalizedoligomers, wherein the resin is configured to react by exposure to lightto form a cured material; wherein the components of the resin can becombined and stored in a single pot for at least 6 months at roomtemperature with no more than with no more than 100% increase in theviscosity of the resin.

Another embodiment includes a photopolymerizable resin for additivemanufacturing comprising: a blocked isocyanates; less than about 5% of astabilized thiol; and at least about 50% of one or more monomers;wherein the resin is configured to react by exposure to light to form acured material, wherein a layer of the resin about 100 μm thick isconfigured to form a cured material in no more than 30 seconds; whereinthe cured material has a toughness in the range about 3-100 MJ/m³ and astrain at break in the range about 30-1000%.

Another embodiment includes an article manufactured from or comprisingany of the photopolymerizable resins disclosed herein.

DETAILED DESCRIPTION

Resins of the disclosure comprise “sealed” or blocked isocyanates, whichin some embodiments, may provide desirable properties related tocrosslink density and/or crystallinity of cured resins. In some cases,the resin mixture may have one or more desirable properties related toshelf-stability, viscosity, print and curing speed, or odor. Such resinsmay be used in the manufacture of articles made by additivemanufacturing (e.g., 3D printing). Some of the properties of the curedresins may include high elongation, flexibility, and toughness, which inturn can be suitable for a number of manufactured articles. For example,a nonlimiting list of manufactured articles include a footwear midsole,a shape memory foam, an implantable medical device, a wearable article,an automotive seat, a seal, a gasket, a damper, a hose, and/or afitting. The resin may comprise a number of components, as describedherein.

For example, one embodiment of the invention includes aphotopolymerizable resin for additive manufacturing, the resincomprising: a blocked isocyanate; and a multifunctional nucleophile.Another embodiment includes a photopolymerizable resin for additivemanufacturing, the resin comprising: a blocked isocyanate; at least onemonomer or oligomer; and a multifunctional nucleophile.

Blocked isocyanates (or “sealed isocyanates”) are molecules thatcomprise isocyanate functionalities which exist in a nonreactivechemical state but which may be unblocked (or “unsealed”) by theapplication of an external stimulus (e.g., heat or light), such that thenonreactive isocyanate species can be reformed into reactive isocyanatespecies. Isocyanates can be blocked, for example, by cyclization (i.e.reaction of the isocyanate with itself to form a dimer or trimer), byreaction with a urea to form a biuret, by reaction with a urethane toform an allophanate, or by reaction with a blocking agent to endcap theisocyanate functionalities. The blocked isocyanate may includemonofunctional blocked isocyanates or polyfunctional blocked isocyanatessuch as monomers, dimers, trimers, etc.

Blocked isocyanates may include multifunctional -mer configurations ofisocyanates, such as uretdione (dimerized isocyanates), biuret,allophanates, or isocyanaurates (trimerized isocyanates). Isocyanatescan react with themselves to form dimers (uretdione) or trimers(isocyanaurates). For example, the blocked isocyanate may include auretdione of hexamethylene diisocyanate (HDI-dimer), a uretdione ofisophorone diisocyanate (IDI-dimer), a uretdione of methylenedicyclohexyl diisocyanate (MDI-dimer), a uretdione of hydrogenatedmethylene dicyclohexyl diisocyanate (HMDI-dimer), and/or a uretdione oftoluene diisocyanate (TDI-dimer). Further, the blocked isocyanate mayinclude an isocyanaurate of hexamethylene diisocyanate (HDI-trimer), anisocyanaurate of isophorone diisocyanate (IDI-trimer), an isocyanaurateof methylene dicyclohexyl diisocyanate (MDI-trimer), an isocyanaurate ofhydrogenated methylene dicyclohexyl diisocyanate (HMDI-trimer), and/oran isocyanaurate of toluene diisocyanate (TDI-trimer). Upon applicationof an external stimulus (e.g., heat or light), the blocked (nonreactive)isocyanate species can be reformed into a reactive isocyanate speciesthrough thermal reorganization.

Isocyanates can react with urea to form biuret. For example, the blockedisocyanate may include a biuret of hexamethylene diisocyanate(HDI-biuret), a biuret of isophorone diisocyanate (IDI-biuret), a biuretof methylene dicyclohexyl diisocyanate (MDI-biuret), a biuret ofhydrogenated methylene dicyclohexyl diisocyanate (HMDI-biuret), and/or abiuret of toluene diisocyanate (TDI-biuret). The blocked isocyanate maycomprise a mixture of isocyanates in a variety of chemicalconfigurations and blocking agents. For example, the production ofHDI-dimer may also produce a small amount of biuret (HDI-biuret) whichis present in the uretdione mixture. Upon application of an externalstimulus (e.g., heat or light), the blocked (nonreactive) isocyanatespecies can be reformed into a reactive isocyanate species through theliberation of the urea group.

Isocyanates can react with urethane to form allophanate. For example,the blocked isocyanate may include an allophanate of hexamethylenediisocyanate (HDI-allophanate), an allophanate of isophoronediisocyanate (IDI-allophanate), an allophanate of methylene dicyclohexyldiisocyanate (MDI-allophanate), an allophanate of hydrogenated methylenedicyclohexyl diisocyanate (HMDI-allophanate), and/or an allophanate oftoluene diisocyanate (TDI-allophanate). Upon application of an externalstimulus (e.g., heat or light), the blocked (nonreactive) isocyanatespecies can be reformed into a reactive isocyanate species through theliberation of the urethane group.

In some cases, the blocked isocyanate may include an isocyanate and ablocking agent. Blocked isocyanates may be formed by the reaction of anisocyanate and a blocking agent. In some cases, the isocyanate may beconfigured to react with the blocking agent, such that isocyanatefunctional groups of the isocyanate are end capped. For example,isocyanates may include, but are not limited to: hexamethylenediisocyanate (HDI), isophorone diisocyanate (IDI), methylenedicyclohexyl diisocyanate (MDI), hydrogenated methylene dicyclohexyldiisocyanate (HMDI), and toluene diisocyanate (TDI). Some examples ofblocking agents may include nucleophiles, derivatives of alcohols,hindered amines, caprolactams, phenols, oximes, and/or pyrazolesmalonates. Upon application of an external stimulus (e.g., heat orlight), the blocked (nonreactive) isocyanate species can be reformedinto a reactive isocyanate species through the liberation of theblocking group. Once in its reactive R—NCO form, the unblockedisocyanate may react with nucleophiles.

The multifunctional nucleophile may be any compound that includes one ormore chemical moieties and nucleophilic group. The multifunctionalnucleophile may react with components of the resin mixture to form apolymer. During storage, the blocked isocyanate may not interact withthe multifunctional nucleophile. In some cases, the multifunctionalnucleophile includes at least one of a multifunctional alcohol, amultifunctional thiol, and/or a multifunctional amine. In specificcases, the multifunctional nucleophile includes a secondary thiol. Insome cases, the secondary thiol includes at least one of Pentaerythritoltetrakis (3-mercaptobutylate); 1,4-bis (3-mercaptobutylyloxy) butane;and/or 1,3,5-Tris(3-melcaptobutyloxethyl)-1,3,5-triazine. In othercases, the multifunctional alcohol is a polyol.

The resin may react by exposure to light to form a cured material. Theblocked isocyanate may be configured to form crosslinks within the curedmaterial. Heat treatment may be applied to the cured material tounblock/liberate blocked isocyanates such that the crosslinks they hadformed are cleaved. Thus, heat treatment may decrease the crosslinkdensity of the cured material. The temperature and duration of heattreatment may be tuned to adjust the amount of blocked isocyanatecrosslinks cleaved. Heat treatment may decrease crosslink density of thecured material by between about 10-100%. Further, the liberatedisocyanates can form urethane polymers, that may agglomerate for formcrystallites. Heat treatment may increase crystallinity of the curedmaterial by between about 10-100%. In some embodiments, the resin maycomprise a blocked isocyanate dimer functionalized with acrylatemoieties, wherein the resin has a viscosity at room temperature of lessthan 1,000 cP. The resin may react by exposure to light to form a curedmaterial, wherein the isocyanate dimer may form crosslinks within thecured material. Thermal treatment of the cured material may liberate theblocked isocyanate dimer, thereby cleaving crosslinks and/or formingcrystalline or semi-crystalline species.

Another embodiment of the invention includes a photopolymerizable resinfor additive manufacturing (e.g., 3D printing), the resin comprising: ablocked isocyanate; and at least one monomer and/or oligomer, whereinthe resin (i.e., resin components) is configured to react by exposure tolight to form a cured material.

In some cases, the resin includes at least one monomer and/or oligomer.In some embodiments, the at least one monomer and/or oligomer is 1-95%by weight of the resin. In other cases, the at least one monomer and/oroligomer is >1%, 1.0-4.99%, 5-10% or about 20%, 30%, 40%, 50%, 60%, 70%,80%, or 90% by weight of the resin. The monomer may include smallmolecules that combine with each other to form an oligomer or polymer.The monomer may include bifunctional monomers having two functionalgroups per molecule and/or polyfunctional monomers having more than onefunctional group per molecule. The oligomer may include moleculesconsisting of a few monomer units. For example, in some cases, theoligomer may be composed of two, three, or four monomers (i.e., dimer,trimer, or tetramer). The oligomer may include bifunctional oligomershaving two functional groups per molecule and/or polyfunctionaloligomers having more than one functional group per molecule.

The at least one monomer and/or oligomer may be capable of reacting withthe other resin components to form a connected polymer network. Forexample, the at least one monomer and/or oligomer may include one ormore functional groups capable of reacting with the two or more reactivegroups of the crosslinking component. The at least one monomer and/oroligomer may include an acrylic functional group. For example, amethacylate, acrylate or acrylamide functional group.

In some cases, at least one monomer and/or oligomer includes one or moremonomers. For example, the one or more monomers may be about 1-95% byweight of the resin. Or, the resin may comprise at least about 50% or atleast about 60% of one or more monomers. In other cases, at least onemonomer and/or oligomer includes an acrylic monomer. The acrylic monomermay have a molecular weight less than 200 Da, less than 500 Da, or lessthan 1,000 Da. The acrylic monomer may include at least one of2-ethylhexyl acrylate, hydroxypropyl acrylate, cyclic trimethylolpropaneformal acrylate, isobornyl acrylate, butyl acrylate, and/orN,N-Dimethylacrylamide. In some cases, the photopolymerizable resin maycomprise at least one monomer and/or oligomer, wherein each monomerand/or oligomer may be an acrylic monomer, a thiol monomer and/or an-ene monomer.

The photopolymerizable resin may demonstrate improved shelf-stability.Resin compositions containing thiols and non-thiol reactive species suchas -enes and acrylates may undergo a dark reaction (i.e, an ambientthermal free-radical polymerization or Michael Addition), which reducesthe shelf-life of these compositions. To account for lower shelf-life ofthese resins, they may either be stored under cold conditions or as atwo-pot system. By contrast, thiol-acrylate resins such as those of thedisclosed materials may include a stabilized thiol (e.g., a secondarythiol). The stabilized thiol may have decreased reactivity, which canpotentially increase the shelf-life of 3D printable resin compositionsand enable storage as a single-pot resin system at room temperature.Moreover, the resin remaining at completion of a 3D printing run may bereused in a subsequent run.

Stabilized thiols may include any thiol that exhibits fewer ambientthermal reactions (e.g., nucleophilic substitution with monomers oroligomers) compared to other thiols. In some cases, the stabilized thiolincludes a bulky side chain. Such bulky side chains may include at leastone chemical group, such as a C1-C18 cyclic, branched, or straightalkyl, aryl, or heteroaryl group. In some cases, the stabilized thiolincludes a secondary thiol. In other cases, the stabilized thiolincludes a multi-functional thiol. In some cases, the stabilized thiolincludes at least one of a difunctional, trifunctional, and/ortetrafunctiorial thiol. In some embodiments, the stabilized thiolincludes at least one of a Pentaerythritol tetrakis(3-mercaptobutylate); and/or 1,4-bis (3-mercaptobutylyloxy) butane.

Another embodiment of the invention includes a storage-stablephotopolymerizable resin mixture, the resin mixture comprising: at leastone monomer and/or oligomer; and a blocked isocyanate, wherein theblocked isocyanate is configured to liberate the reactive isocyanatefunctionality during or after exposure of the resin to light, whereinthe components of the resin mixture can be combined and stored (forexample, in a single pot) for at least 6 months at room temperature withno more than 2%, 5%, 10%, 25%, 50% or 100% increase in the viscosity ofthe resin.

Another embodiment of the invention includes a storage-stablephotopolymerizable resin mixture, the resin mixture, comprising: atleast one monomer and/or oligomer; and a blocked isocyanate, wherein theblocked isocyanate is configured to liberate the reactive isocyanatefunctionality during exposure of the resin to light, wherein thecomponents of the resin mixture can be combined and stored in a singlepot for at least 1 week at room temperature with no more than 2%, 5%,10%, 25%, 50% or 100% increase in the viscosity of the resin.

In other embodiments, the disclosure provides a storage-stablephotopolymerizable resin mixture, the resin mixture comprising: at leastone monomer and/or oligomer; and a blocked isocyanate, wherein theblocked isocyanate is configured to liberate the reactive isocyanatefunctionality after exposure of the photopolymerizable resin to lightwherein the components of the resin mixture can be combined and storedin a single pot for at least 1 week at room temperature with no morethan 2%, 6%, 10%, 25%, 50% or 100% increase in the viscosity of theresin.

The stability of the resin mixture may be tuned by inclusion of astabilized thiol. In some cases, the photopolymerizable resin isconfigured for continuous use in a 3D printing operation in an airenvironment for a period of 1 month without an increase in viscosity ofmore than 2%, 5%, 10%, 25%, 50% or 100%. In some cases, thephotopolymerizable is configured for continuous use in a 3D printingoperation in an air environment for a period of 3 months without anincrease in viscosity of more than 10%. In some cases, thephotopolymerizable resin is configured for continuous use in a 3Dprinting operation in an air environment for a period of 6 monthswithout an increase in viscosity of more than 10%. In some cases, thephotopolymerizable resin a is configured for continuous use in a 3Dprinting operation in an air environment for a period of 1 year withoutan increase in viscosity of more than 10%. In some cases, thephotopolymerizable resin is configured for continuous use in a 3Dprinting operation in an air environment for a period of 2 years withoutan increase in viscosity of more than 10%.

The cured materials in the present disclosure may provide mechanicalproperties that are tough and flexible (measured, e.g., by percentstrain at break or strain capacity) that may be suitable for use inmanufactured articles in which these properties are desired (e.g., shoemidsoles, insoles, outsoles). Articles comprising these cured materialsmay thus be produced at reduced expense with more possible efficiencyand customizability of article designs and mechanical properties in anadditive manufacturing process.

Specifically, toughness may be customized by controlling the percentageand type of monomers with optional combination of additional oligomers,fillers, and additives. Control of these parameters may allow specificdesign of the materials elongation capacity (strain) and the force atwhich this elongation occurs (stress). Taken together, the stress/strainbehavior of a material may impact its fracture toughness.

Additionally, the strain at break may be customized by controlling thepercentage and type of monomers with optional combination of additionaloligomers, fillers, and additives. Control of the underlying networkmorphology, the density between crosslinks, and the tear strength of thematerial (enabled by filler and matrix-filler interactions) may allowcontrol over the elongation (strain) of the material. In some cases, thecured material has a strain at break of about 100%. In some cases, thecured material has a strain at break of about 200%. In some cases, thecured material has a strain at break of about 300%. In some cases, thecured material has a strain at break of about 400%. In some cases, thecured material has a strain at break of about 500%. In some cases, thecured material has a strain at break of about 600%. In some cases, thecured material has a strain at break of about 700%. In some cases, thecured material has a strain at break of about 800%.

Some embodiments of the disclosure include a photopolymerizable resinfor additive manufacturing, the resin comprising: a blocked isocyanate,and at least one monomer and/or oligomer, wherein the resin isconfigured to react by exposure to light to form a cured material;wherein the cured material has a strain capacity of about 10%. In somecases, the cured material has a strain capacity of about 30%, about 50%,about 100%, about 200%, about 300%, or about 500%.

The resin mixture may be liquid, solid, or semi-solid. In some cases,the solid resin mixture may be in powder form. Powders may be processedvia Selective Laser Sintering (SLS). Some embodiments of the inventionprovide, a powder composition for additive manufacturing, the powdercomprising: a powdered blocked isocyanate, and a powdered polyol. Otherembodiments provide a powder composition for additive manufacturing, thepowder comprising: a powdered blocked isocyanate, and a powdered diol.

The molecular weight of the powdered polyol may be in the range about500-20,000 Daltons. The powdered polyol may include a powdered did, forexample semi-crystalline powdered diols. The powdered polyol may includehydroxy functionalized polymers and/or oligomers. In some cases, thepowdered polyol may include oligomer and/or polymer diols ofpolycaprolactones, polylactides, polyethylene glycols, polyurethanes,etc.

In some cases, the powdered blocked isocyanate may include amultifunctional aromatic blocked isocyanate. In some cases, the powderedblocked isocyanate includes coronates. The powder composition mayfurther comprise a powdered polymer. In some cases, the powdered polymerincludes nylons, urethanes, polyesters, polyethylenes, polypropylenes,poly lactic acid, and/or polycaprolactones.

Some embodiments of the invention may include a photopolymerizable resinfor additive manufacturing, the resin comprising: about 1-20% of athiol; about 30-90% of an acrylic monomer; about 1-70% of a blockedisocyanate; wherein the resin is configured to react by exposure tolight to form a cured material.

In some cases, the thiol includes a secondary thiol. In specific cases,the secondary thiol includes at least one of Pentaerythritol tetrakis(3-mercaptobutylate); 1,4-bis (3-mercaptobutylyloxy) butane; and/or1,3,5-Tris(3-melcaptobutyloxethyl)-1,3,5-triazine. In some cases, theacrylic monomer includes at least one of 2-ethylhexyl acrylate,hydroxypropyl acrylate, cyclic trimethylolpropane formal acrylate,isobornyl acrylate, butyl acrylate, and/or N,N-Dimethylacrylamide. Insome cases, the blocked isocyanate includes an isocyanate and a blockingagent. In specific cases, the isocyanate includes, HDI, IDI, MDI, HDMIand/or TDI. In some cases, the blocked isocyanate includes uretdione,biuret, allophphanates, and/or isocyanaurates. In some cases, blockingagent includes dimer isocyanates and/or trimer isocyanates. In specificcases, the blocking agent includes derivatives of alcohols, hinderedamines, caprolactams, phenols, oximes, and/or pyrazoles malonates.

The resin viscosity may be any value that facilitates use in additivemanufacturing (e.g., 3D printing) of an article. Higher viscosity resinsare more resistant to flow, whereas lower viscosity resins are lessresistant to flow. Resin viscosity may affect, for example,printability, print speed or print quality. For example, the 3D printermay be compatible only with resins having a certain viscosity. Or,increasing resin viscosity may increase the time required to smooth thesurface of the deposited resin between print layers because the resinmay not settle out as quickly.

The thiol-acrylate photopolymerizable resin of the disclosed materialsmay also possess a high cure rate and low viscosity. Additivemanufactured objects are created by building up materialslayer-by-layer. Each layer is built by depositing liquid resin andapplying light to photocure. The viscosity and cure rate of the resin,therefore, affect print speed. A low viscosity resin will quickly spread(e.g., 1-30 seconds) into a flat layer, without the need to apply heator mechanically manipulate the layer. The spread can be faster (e.g.,1-10 seconds) with mechanical manipulation. Additionally, lowerviscosity may allow faster movement of the recoating blade. The fasterthe cure rate, the more quickly a next, subsequent layer can be built.

The resin viscosity may be tuned, for example, by adjusting the ratio ofmonomers to oligomers. For example, a resin having higher monomercontent may exhibit a lower viscosity. This may be because the lowermolecular weight monomers are able to solvate the oligomers, decreasingoligomer-oligomer interactions and thus decreasing the overall resinviscosity. The resin may have a viscosity at or above room temperatureof less than about 250 centipoise, less than about 500 centipoise, lessthan about 750 centipoise, or less than about 1,000 centipoise. In somecases, the resin has a viscosity at a temperature between 0° C. and 80°C. of less than about 1000 centipoise, less than about 500 centipoise,or less than about 100 centipoise. In some cases, the resin has aviscosity at or above room temperature of less than about 1000centipoise, less than about 500 centipoise, or less than about 100centipoise.

Another aspect of the invention provides a 3D printable resin which isable to be printed with high crosslink density and, after printing, canhave crosslinks selectively cleaved to enable lower crosslink density,and thus higher elongation. This may be accomplished by post-treatingcured materials comprising the blocked isocyanate, such that isocyanatemay be liberated, thus cleaving crosslinks in the cured material. Insome cases, the cured material is post-treated with heat. In specificcases, the cured material is post-treated with heat, such that crosslinkdensity of the polymer network is decreased by an amount proportional toor less than the % composition of the resin equal to the total amount ofblocked isocyanate crosslinking molecules within the resin mixture. Insome cases, the cured material has a strain capacity of about 10%, 30%,50%, 100%, 200%, 300%, or 500%.

Another aspect of the invention provides a resin which may becomecrystalline or semi-crystalline with a high melt temperature afterprinting. Such crystallinity may enable thermoplastic polymers to betough, providing transient, physical crosslinks that can break andreform to dissipate energy as may be desired. In some cases, the curedmaterial is post-treated with heat, such that crystallinity of thepolymer network is increased by an amount proportional to or less thanthe % composition of the resin equal to the total amount of blockedisocyanate molecules within the resin mixture. In some cases, the curedmaterial has a crystal fraction of about 1, about 10% or about 25%.

Another embodiment of the invention includes a photopolymerizable resinfor additive manufacturing, the resin comprising: a blocked isocyanate,and a polyol, wherein the resin includes the blocked isocyanate and thepolyol in about a stoichiometric ratio.

In some cases, the polyol has a molecular weight greater than about 100Daltons, about 500 Daltons, about 1000 Daltons, about 2000 Daltons, orabout 5000 Daltons.

A photopolymerizable resin for additive manufacturing, the resincomprising: a blocked isocyanate, and a thiol, wherein the resinincludes the blocked isocyanate and the polyol in about a stoichiometricratio. In some cases, the isocyanate is configured to react with theblocking agent, such that functional groups of the isocyanate are endcapped. In some cases, the thiol includes a difunctional thiol or amultifunctional thiol. In some cases, the thiol includes a secondarythiol. In some cases, the thiol has a molecular weight greater thanabout 100 Daltons, about 500 Daltons, about 1000 Daltons, about 2000Daltons, or about 5000 Daltons.

Another embodiment of the invention provides a photopolymerizable resinfor additive manufacturing in an oxygen environment, the resincomprising: a blocked isocyanate; a crosslinking component; at least onemonomer and/or oligomer; and a chain transfer agent comprising at leastone of a thiol, a secondary alcohol, and/or a tertiary amine, whereinthe resin is configured to react by exposure to light to form a curedmaterial, wherein the chain transfer agent is configured to permit atleast some bonding between a layer of resin previously cured and anadjacent, subsequently cured layer of resin, despite an oxygen-richsurface present on the previously cured layer of resin at an interfacebetween the previously cured layer of resin and the subsequently curedlayer of resin. In some cases, bonding is covalent, crosslinking, orphysical entanglement of polymer chains.

The crosslinking component may include any compound that reacts byforming chemical or physical links (e.g., ionic, covalent, or physicalentanglement) between the resin components to form a connected polymernetwork. The crosslinking component may include two or more reactivegroups capable of linking to other resin components. For example, thetwo or more reactive groups of the crosslinking component may be capableof chemically linking to other resin components. The crosslinkingcomponent may include terminal reactive groups and/or side chainreactive groups. The number and position of reactive groups may affect,for example, the crosslink density and structure of the polymer network.

The two or more reactive groups may include an acrylic functional group.For example, a methacylate, acrylate or acrylamide functional group. Insome cases, the crosslinking component includes a difunctional acrylicoligomer. For example, the crosslinking component may include anaromatic urethane acrylate oligomer or an aliphatic urethane acrylateoligomer. The crosslinking component may include at least one of CN9167,CN9782, CN9004, poly(ethylene glycol) diacrylate, bisacrylamide,tricyclo[5.2.1.0^(2,6)]decanedimethanol diacrylate, and/ortrimethylolpropane triacrylate. The size of the crosslinking componentmay affect, for example, the length of crosslinks of the polymernetwork.

The number of crosslinks or crosslink density may be selected to controlthe properties of the resulting polymer network. For example, polymernetworks with fewer crosslinks may exhibit higher elongation, whereaspolymer networks with greater crosslinks may exhibit higher rigidity.This may be because the polymer chains between the crosslinks maystretch under elongation. Low crosslink-density chains may coil up onthemselves to pack more tightly and to satisfy entropic forces. Whenstretched, these chains can uncoil and elongate before pulling oncrosslinks, which may break before they can elongate. In highlycrosslinked materials, the high number of crosslinked chairs may lead tolittle or no uncoilable chain length and nearly immediate bond breakageupon strain.

The amount of the crosslinking component may be selected to control thecrosslink density and resulting properties of the polymer network. Insome cases, the crosslinking component is 1-95% by weight of the resin.In other cases, the crosslinking component is >1%, 1.0-4.99%, 5-10% orabout 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% by weight of the resin.

In some cases, the resin includes at least one monomer and/or oligomer.In some embodiments, the at least one monomer and/or oligomer is 1-95%by weight of the resin. In other cases, the at least one monomer and/oroligomer is >1%, 1.0-4.99%, 5-10% or about 20%, 30%, 40%, 50%, 60%, 70%,80%, or 90% by weight of the resin. The monomer may include smallmolecules that combine with each other to form an oligomer or polymer.The monomer may include bifunctional monomers having two functionalgroups per molecule and/or polyfunctional monomers having more than onefunctional group per molecule. The oligomer may include moleculesconsisting of a few monomer units. For example, in some cases, theoligomer may be composed of two, three, or four monomers (i.e., dimer,trimer, or tetramer). The oligomer may include bifunctional oligomershaving two functional groups per molecule and/or polyfunctionaloligomers having more than one functional group per molecule.

The at least one monomer and/or oligomer may he capable of reacting withthe other resin components to form a connected polymer network. Forexample, the at least one monomer and/or oligomer may include one ormore functional groups capable of reacting with the two or more reactivegroups of the crosslinking component. The at least one monomer and/oroligomer may include an acrylic functional group. For example, amethacylate, acrylate or acrylamide functional group.

In some cases, at least one monomer and/or oligomer includes one or moremonomers. For example, the one or more monomers may be about 1-95% byweight of the resin. Or, the resin may comprise at least about 50% or atleast about 60% of one or more monomers. In other cases, at least onemonomer and/or oligomer includes an acrylic monomer. The acrylic monomermay have a molecular weight less than 200 Da, less than 500 Da, or lessthan 1,000 Da. The acrylic monomer may include at least one of2-ethylhexyl acrylate, hydroxypropyl acrylate, cyclic trimethylolpropaneformal acrylate, isobornyl acrylate, butyl acrylate, and/orN,N-Dimethylacrylamide.

Chain transfer agents may include any compound that possesses at leastone weak chemical bond that potentially reacts with a free-radical siteof a growing polymer chain and interrupts chain growth. In the processof free radical chain transfer, a radical may be temporarily transferredto the chain transfer agent which reinitiates growth by transferring theradical to another component of the resin, such as the growing polymerchain or a monomer. The chain transfer agent may affect kinetics andstructure of the polymer network. For example, the chain transfer agentmay delay formation of the network. This delayed network formation mayreduce stress in the polymer network leading to favorable mechanicalproperties.

The chain transfer agent may comprise at least one of a thiol, asecondary alcohol, and/or a tertiary amine. The secondary alcohol mayinclude at least one of isopropyl alcohol, and/or hydroxypropylacrylate. In some cases, the thiol is about 0.5% to 4.0%, 4.0% to 4.7%,4.7% to 4.99%, 4.99-5%, or 5-50% by weight of the resin. The thiol mayinclude a secondary thiol. The secondary thiol may include at least oneof Pentaerythritol tetrakis (3-mercaptobutylate); 1,4-bis(3-mercaptobutylyloxy) butane; and/or1,3,5-Tris(3-melcaptobutyloxethyl)-1,3,5-triazine. The tertiary aminemay include at least one of aliphatic amines, aromatic amines, and/orreactive amines. The tertiary amine may include at least one of triethylamine, N,N′-Dimethylaniline, and/or N,N′-Dimethylacrylamide.

In some cases, the chain transfer agent may be configured to react withan oxygen radical to initiate growth of at least one new polymer chainand/or reinitiate growth of a polymer chain terminated by oxygen. Forexample, the chain transfer agent may include a weak chemical bond suchthat the radical may be displaced from the oxygen radical andtransferred to another polymer, oligomer or monomer.

Additive manufacturing processes, such as 3D printing, may produce threedimensional objects by sequentially curing layers of aphotopolymerizable resin. Thus, articles produced by additivemanufacturing may comprise a majority or plurality of photocured layers.Additive manufacturing may be performed in an oxygen environment,wherein oxygen may diffuse into a deposited layer of resin.

In some cases, an oxygen radical may be formed by a reaction of diffusedoxygen with a growing polymer chain. For example, at the oxygen-richsurface of a layer of resin, oxygen may react with initiator radicals orpolymer radicals to form an oxygen radical. The oxygen radical may beaffixed to a polymer side chain. Oxygen radicals, for example, peroxyradicals, may slow down curing of the resin. This slowed curing maylead, for example, to the formation of a thin, sticky layer of uncuredmonomers and/or oligomers at the oxygen-rich surface of a previouslycured layer of resin, which would otherwise minimize adhesion to anadjacent subsequently cured layer of resin. the oxygen radical isaffixed to a polymer side chain.

In some cases, chain transfer agent is configured to react with anoxygen radical to initiate growth of at least one new polymer chain. Infurther cases, the oxygen radical may be a peroxy radical. In furthercases, the oxygen radical is formed by a reaction of diffused oxygenwith a growing polymer chain. In some cases, chain transfer agent isconfigured to reinitiate growth of a polymer chain terminated by oxygen.In some cases, the chain transfer agent is configured to transfer aradical from a first polymer chain or chain branch within a previouslycured resin layer to a second polymer chain or chain branch within thevolume of the photopolymerizable resin. In some cases, the chaintransfer agent is configured to promote growth of at least one newpolymer chain near the oxygen-rich surface present on the previouslycured layer of resin.

Due at least in part to the presence of a chain transfer agent, at leastsome bonding between a layer of resin previously cured and an adjacent,subsequently cured layer of resin, may occur despite an oxygen-richsurface present on the previously cured layer of resin at an interfacebetween the previously cured layer of resin and the subsequently curedlayer of resin. In some cases, the bonding may be covalent. In someembodiments, the bonding may be ionic. In some cases, the bonding may bephysical entanglement of polymer chains. Additionally, in some cases,the chain transfer agent is ½-50% by weight of resin. In some cases, thechain transfer agent is about 0.5-4.0%, 4.0-4.7%, 4.7-4.99%, 4.99-5%, or5-50% by weight of the resin.

The resin materials may exhibit excellent interlayer strength when 3Dprinted in air environments. Because three-dimensional prints are builtlayer by layer, when printing in open-air, each resin layer will have anopportunity (e.g., during patterning) to become enriched with oxygen atits surface exposed to air. With prior resins, this oxygen enrichmentresulted in weak adhesion between layers because the oxygen available atthe oxygen-rich interfaces between layers inhibited free-radicalpolymerization, thereby limiting chain growth and retarding thereaction. The photopolymerizable resins of the present invention,however, may include a secondary thiol that can overcome this problemand promote the chemical and physical crosslinking between 3D printedlayers even in the presence of elevated or ambient oxygen levels at theinterfaces between layers.

Further, the resin materials may demonstrate lower sensitivity tooxygen. In free-radical polymerization systems, oxygen reacts withprimary initiating or propagating radicals to form peroxy radicals. Inprior resins, these peroxy radicals would tend to terminatepolymerization. In the thiol-acrylate photopolymerizable resins,however, thiols may act as a chain transfer agent allowing for furtherpropagation of the polymerization reaction. Lower sensitivity to oxygenmay enable open-air manufacturing processes without the expense ofreduced-oxygen manufacturing (e.g., a nitrogen or argon blanket).

Any suitable additive compounds may be optionally added to the resin.For example, the resin may further comprise poly(ethylene glycol). Theresin may further comprise polybutadiene. The resin may further comprisepolydimethylsiloxane acrylate copolymer. The resin may further comprisepoly(styrene-co-maleic anhydride).

The resin may further comprise a photoinitiator, an inhibitor, a dye,and/or a filler. The photoinitiator may be any compound that undergoes aphotoreaction on absorption of light, producing a reactive free radical.Therefore, photoinitiators may be capable of initiating or catalyzingchemical reactions, such as free radical polymerization. Thephotoinitiator may include at least one ofPhenylbis(2,4,6-trimethylbenzoyl)phosphine oxide,Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, Bis-acylphosphineoxide, Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and/or2,2′-Dimethoxy-2-phenylacetophenone. In some cases, the photoinitiatoris 0.01-3% by weight of the resin.

The inhibitor may be any compound that reacts with free radicals to giveproducts that may not be able to induce further polymerization. Theinhibitor may include at least one of Hydroquinone,2-methoxyhydroquinone, Butylated hydroxytoluene, Diallyl Thiourea,and/or Diallyl Bisphenol A.

The dye may be any compound that changes the color or appearance of aresulting polymer. The dye may also serve to attenuate stray lightwithin the printing region, reducing unwanted radical generation andovercure of the sample. The dye may include at least one of2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene, Carbon Black, and/orDisperse Red 1.

The filler may be any compound added to a polymer formulation that mayoccupy the space of and/or replace other resin components. The fillermay include at least one of titanium dioxide, silica, calcium carbonate,clay, aluminosilicates, crystalline molecules, crystalline oligomers,semi-crystalline oligomers, and/or polymers, wherein said polymers arebetween about 1,000 Da and about 20,000 Da molecular weight.

An article may be made from the resin as described in any embodiment.The article may be made by cast polymerization or additive manufacturingprocesses, such as 3D printing. The article may include footwearmidsole, a shape memory foam, an implantable medical device, a wearablearticle, an automotive seat, a seal, a gasket, a damper, a hose, and/ora fitting. An article may be made having a majority of layers comprisingthe resin as described in any embodiment.

In some embodiments, an article may be made from the resin as describedin any embodiment that further includes a surface coating. The surfacecoating may be applied to an article for potentially obtaining desiredappearance or physical properties of said article. The surface coatingmay comprise a thiol. The surface coating may comprise a secondarythiol. The surface coating may comprise an alkane. The surface coatingmay comprise a siloxane polymer. The surface coating may comprise atleast one of semi-fluorinated poly ether and/or per-fluorinated polyether.

The glass transition temperature (T_(g)) of the cured material is thetemperature at which a polymer goes from an amorphous rigid state to amore flexible state. The glass transition temperature of the curedmaterial may be customized by controlling the percentage and type ofmonomer, the percentage and type of oligomer, filler, plasticizer andcuring additives (e.g., dye, initiator, or inhibitor). In some cases,the cured material has a glass transition temperature in the range about10° C. to about −30° C. In some cases, the cured material has a glasstransition temperature with a full width half max of more than 50° C. Insome cases, the resin has a glass transition temperature with a fullwidth half max of less than 50° C. In some cases, the resin has a glasstransition temperature less than about 0° C. or greater than about 80°C.

In some cases, the article has a tensile strength in the Z-directionwithin about 33% of the tensile strength in the X-direction. In othercases, the article has a tensile strength in the Z-direction withinabout 10% of the tensile strength in the X-direction. In other cases,the article has a tensile strength in the Z-direction within about 5% ofthe tensile strength in the X-direction. In other cases, the article hasa compressive strength in the Z-direction within about 33% of thecompressive strength in the X-direction. In other cases, the article hasa compressive strength in the Z-direction within about 10% of thecompressive strength in the X-direction. In other cases, the article hasa compressive strength in the Z-direction within about 5% of thecompressive strength in the X-direction.

Another embodiments of the invention provides a photopolymerizable resinfor additive manufacturing printing in an oxygen environment, the resincomprising: a blocked isocyanate; a photoinitiator, wherein thephotoinitiator is configured to generate a free radical after exposureto light; a crosslinking component; and at least one monomer and/oroligomer, wherein the crosslinking component and the at least onemonomer and/or oligomer are configured to react with the free radical toprovide growth of at least one polymer chain radical within a volume ofthe photopolymerizable resin, wherein the at least one polymer chainradical reacts with diffused oxygen to provide an oxygen radical; and achain transfer agent comprising at least one of a thiol, a secondaryalcohol, and/or a tertiary amine, wherein the chain, transfer agent isconfigured to transfer the oxygen radical to initiate growth of at leastone new polymer chain radical.

In some embodiments, the photoinitiator may be configured to generate afree radical after exposure to light. In some embodiments, thecrosslinking component and the at least one monomer and/or oligomer areconfigured to react with the free radical to provide growth of at leastone polymer chain radical within a volume of the photopolymerizableresin. In some embodiments, the at least one polymer chain radicalreacts with diffused oxygen to provide an oxygen radical. In someembodiments, the chain transfer agent may be configured to transfer theoxygen radical to initiate growth of at least one new polymer chainradical.

In some embodiments, the crosslinking component and the at least onemonomer and/or oligomer are configured to react to provide one or morepolymer chains after exposure to light. In some embodiments, the chaintransfer agent may be configured to transfer a free radical associatedwith the one of the polymer chains to another one of the polymer chains.

In some embodiments, the photoinitiator may be configured to generate afree radical after exposure to light wherein the free radical initiatesa chain reaction between the crosslinking component and the at least onemonomer and/or oligomer to provide one or more polymer chains within avolume of the photopolymerizable resin. In some embodiments, the chaintransfer agent may be configured to reinitiate the chain reaction toprovide one or more new polymer chains within a volume of thephotopolymerizable resin.

Another embodiment of the invention includes a photopolymerizable resin,the resin comprising: a blocked isocyanate; a crosslinking component; atleast one monomer and/or oligomer, wherein the crosslinking componentand the at least one monomer and/or oligomer are configured to react toprovide one or more polymer chains after exposure to light; and a chaintransfer agent comprising at least one of a thiol, a secondary alcohol,and/or a tertiary amine, wherein the chain transfer agent is configuredto transfer a free radical associated with the one of the polymer chainsto another one of the polymer chains.

Another embodiment of the invention includes a storage-stablephotopolymerizable resin mixture, the resin mixture comprising: ablocked isocyanate; at least one monomer and/or oligomer, wherein the atleast one monomer and/or oligomer includes one or more acrylic monomers,wherein the one or more acrylic monomers are at least about 50% byweight of the resin; and less than about 5% of a stabilized thiolcomprising one or more thiol functional groups, wherein the stabilizedthiol is configured to inhibit a nucleophilic substitution reactionbetween the one or more thiol functional groups and the one or moremonomers or oligomers, wherein the components of the resin mixture canbe combined and stored in a single pot for at least 6 months at roomtemperature with no more than 2%, 5%, 10%, 25%, 50% or 100% increase inthe viscosity of the resin.

Unblocked isocyanates, in the presence of a nucleophile, may react in amatter of seconds to days (depending on the strength of thenucleophile). If the isocyanate is blocked, it may exist in the presenceof a nucleophile indefinitely. Because the blocking groups are thermallylabile and because temperature is an average of the kinetic energy inthe system, at some time point a blocked isocyanate will becomespontaneously unblocked and react with an available nucleophile and theviscosity will rise. Blocked isocyanates may enable long shelf life withlow viscosity by blocking the reaction of the isocyanate with thepresent nucleophiles.

In some embodiments of the invention, the resin comprises at least about50% of one or more acrylic monomers and about 0-45% of one or moreacrylic-functionalized oligomers. The thiol-acrylate resin can be storedas a single pot system at room temperature. In some cases, thecomponents of the resin can be combined and stored in a single pot(e.g., a suitable container for chemical storage) for at least 6 monthsat room temperature with no more than 10-20% increase in the viscosityof the resin.

Stabilized thiols may be any thiol that exhibits fewer ambient thermalreactions (e.g., nucleophilic substitution with monomers or oligomers)compared to other thiols. In some cases, the stabilized thiol includes abulky side chain. Such bulky side chains may include at least onechemical group, such as a C1-C18 cyclic, branched, or straight alkyl,aryl, or heteroaryl group. In some cases, the stabilized thiol includesa secondary thiol. In other cases, the stabilized thiol includes amulti-functional thiol. In some cases, the stabilized thiol includes atleast one of a difunctional, trifunctional, and/or tetrafunctionalthiol. In some embodiments, the stabilized thiol includes at least oneof a Pentaerythritol tetrakis (3-mercaptobutylate); and/or 1,4-bis(3-mercaptobutylyloxy) butane.

The thiol-acrylate photopolymerizable resin may demonstrate improvedshelf-stability. Resin compositions containing thiols and non-thiolreactive species such as -enes and acrylates may undergo a dark reaction(i.e, an ambient thermal free-radical polymerization or MichaelAddition), which reduces the shelf-life of these compositions. Toaccount for lower shelf-life of these resins, they may either be storedunder cold conditions or as a two-pot system. By contrast,thiol-acrylate resins such as those of the disclosed materials mayinclude a stabilized thiol (e.g., a secondary thiol). The stabilizedthiol may have decreased reactivity, which can potentially increase theshelf-life of 3D printable resin compositions and enable storage as asingle-pot resin system at room temperature. Moreover, the resinremaining at completion of a 3D printing run may be reused in asubsequent run.

In some embodiments of the invention, the components of the resinmixture can be combined and stored in a single pot for at least 6 monthsat room temperature with no more than 10% increase in the viscosity ofthe resin. The increased shelf life, pot life end/or print life may bedue, at least in part, to the presence of a stabilized thiol in theresin mixture. Resin compositions containing thiols and non-thiolreactive species, for example acrylates, can undergo a dark reaction(i.e, ambient thermal free-radical polymerizations or nucleophilicMichael additions). The stabilized thiol, however, may have reducedreactivity in the dark reaction.

In some cases, the resin may be configured for continuous use in a 3Dprinting operation in an air environment for a period of 2 weeks withoutan increase in viscosity of more than 10%. In some cases, the resin maybe configured for continuous use in a 3D printing operation in an airenvironment for a period of 4 weeks without an increase in viscosity ofmore than 10%. In some cases, the resin may be configured for continuoususe in a 3D printing operation in an air environment for a period of 10weeks without an increase in viscosity of more than 10%. In some cases,the resin may be configured for continuous use in a 3D printingoperation in an air environment for a period of 26 weeks without anincrease in viscosity of more than 10%. In some cases, the resin may beconfigured for continuous use in a 3D printing operation in an airenvironment for a period of 1 year without an increase in viscosity ofmore than 10%.

In other cases, the at least one monomer and/or oligomer includes one ormore acrylic monomers. In some embodiments, the one or more acrylicmonomers are at least about 50% by weight of the resin. In other cases,the resin comprises less than about 5% of a stabilized thiol comprisingone or more thiol functional groups, wherein the stabilized thiol may beconfigured to inhibit a nucleophilic substitution reaction between theone or more thiol functional groups and the one or more monomers oroligomers. The stabilized thiol may include at least one of adifunctional, trifunctional, and/or tetrafunctional thiol.

Another embodiment of the invention includes a photopolymerizable resinfor additive manufacturing, the resin comprising: a blocked isocyanate;a crosslinking component; at least one monomer and/or oligomer; aphotoinitiator, wherein the photoinitiator is configured to generate afree radical after exposure to light wherein the free radical initiatesa chain reaction between the crosslinking component and the at least onemonomer and/or oligomer to provide one or more polymer chains within avolume of the photopolymerizable resin; a chain transfer agentcomprising at least one of a thiol, a secondary alcohol, and/or atertiary amine, wherein the chain transfer agent is configured toreinitiate the chain reaction to provide one or more new polymer chainswithin a volume of the photopolymerizable resin, wherein a layer of theresin about 100 μm thick is configured to form a cured material in nomore than 30 seconds; wherein the resin has a viscosity at roomtemperature of loss than 1,000 centipoise.

The cure rate of resin layers may depend on the tendency the resincomponents to polymerize by free radical reactions during curing by alight source (e.g., an ultraviolet light). The resin may optionallycomprise a photoinitiator or inhibitor that may be used to speed orretard the curing process. A layer of resin of the disclosure, whenprovided in a thickness suitable for 3D printing or other additivemanufacturing, may be able to photocure in time lengths desired forefficient production of an article. The cure rate may be such that alayer of the photopolymerizable resin about 100 μm thick is configuredto cure in no more than 30 seconds. For example, in some cases, a layerof the resin about 100 μm thick may be configured to form a curedmaterial in no more than 30 seconds, no more than 20 seconds, no morethan 10 seconds, no more than 3 seconds, no more than 1 second, or nomore than 1/10 of a second. In other cases, a layer of the resin about400 μm thick may be configured to form a cured material in no more than1 second. In other cases, a layer of the resin about 300 μm thick may beconfigured to form a cured material in no more than 1 second. In othercases, a layer of the resin about 200 μm thick may be configured to forma cured material in no more than 1 second. In other cases, a layer ofthe resin about 1000 μm thick may be configured to form a cured materialin no more than 30 seconds. In other cases, a layer of the resin about10 μm thick may be configured to form a cured material in no more than 2seconds, no more than 1 seconds, no more than ½ a second, no more than ¼of a second or no more than 1/10 of a second.

Another embodiment of the invention provides a photopolymerizable resinfor additive manufacturing, the resin comprising: a blocked isocyanate;less than 5% of a thiol; at least about 50% of one or more monomers; anda photoinitiator, wherein the photoinitiator is configured to form afree radical after exposure to light, such that the free radicalinitiates growth of one or more polymer chains including at least thedifunctional and monofunctional monomers; wherein the thiol isconfigured to promote continued growth of the one or more polymerchains, wherein the resin is configured to react by exposure to light toform a cured material, wherein the cured material has a glass transitiontemperature in the range about 5-30° C.

Additionally, the cured material is in a glassy state below the glasstransition temperature, and the cured material is in a tough state abovethe glass transition temperature. In some cases, a tough state occurs inthe range about 5-50° C. In some cases, the tough state occurs in therange about 20-40° C. In some cases, the resin has a glass transitiontemperature is in the range about 20-25° C.

The materials may have a strain at break greater than 100%, up to 1000%.The materials may have a toughness of between about 30 MJ/m³ and about100 MJ/m³. In specific cases, the cured material has a strain at breakin the range about 400-500% at about 20° C. In some cases, the curedmaterial has a glass transition temperature in the range about 10-30° C.In some cases, the cured material has a Shore A hardness of about 30 atabout 20° C. In some cases, the cured material has a Shore A hardness ofabout 19 at about 20° C. In some cases, the cured material in the toughstate has a toughness in the range about 3-30 MJ/m³. In someembodiments, the cured material in the tough state has a toughness inthe range about 30-100 MJ/m³. In some cases, the cured material in theglassy state has an elastic modulus less than 5 GPa, greater than 2 Pa,or greater than 1 GPa. In some cases, the cured material in the glassystate has an elastic modulus between 2 and 5 GPa. These materialproperties may be controlled through the crosslinking density of thesystem and the crystallinity percentage. The crosslinks may enable theultimate strain while the crystals reinforce the matrix, providinghigher strength and longer elongation before break.

Another embodiment of the invention provides a photopolymerizable resinfor additive manufacturing, the resin comprising: a blocked isocyanate;less than about 5% of a thiol; and at least about 50% of one or moremonomers; wherein the resin is configured to react to form a curedmaterial; wherein the cured material has a toughness in the range about3-30 MJ/m³ and a strain at break ranging in the range about 30-300%.

In some cases, the thiol is about 0.5% to 4.0% by weight of the resin,about 4.0% to 4.7% by weight of the resin, about 4.7% to 4.99% by weightof the resin, or about 4.99-5% by weight of the resin.

In some cases, the cured material has a toughness in the range about8-15 MJ/m³ or less than about 1 MJ/m². In some cases, the cured materialhas a strain at break in the range about 50-250%, in some cases, thecured material has a glass transition temperature in the range about10-30° C.

Some embodiments of the invention provides a photopolymerizable resinfor additive manufacturing, the resin comprising: a blocked isocyanate;less than about 5% of a thiol; and at least about 60% of one or moremonomers, wherein the resin is configured to react by exposure to lightto form a cured material; wherein the cured material has a toughness inthe range about 3-100 MJ/m³ and a strain at break in the range about200-1000%.

Another embodiments of the invention provides a photopolymerizable resinfor additive manufacturing, the resin comprising: a blocked isocyanate;at least at least one monomer and/or oligomer; and less than about 20%of a thiol, wherein the resin is configured to react by exposure tolight to provide a cured material, wherein the cured material producesless than 1 part per 100 million of thiol volatiles at ambienttemperature and pressure over 50 seconds in an oxygen environment.

Although thiols have a bad odor, the thiol-acrylate resin may havelittle to no discernable smell. It is thought that the low-smellcharacteristic results, at least in part, from the use of high molecularweight thiols in less than stoichiometric amounts to reduce or eliminatethiol odor. Further, the thiol may become almost completely incorporatedinto the polymer network.

Thiol volatiles may result from cured materials or during manufacturingprocesses that use thiols. The thiol volatiles may be tailored to bebelow thresholds detectable to human scent. This may be achieved, forexample, by the resin comprising less than about 5% of a thiol. Thiolvolatiles may be measured in a sample by use of a gas chromatographymass spectrometer (GC-MS). In some cases, the cured material producesless than 1 part per 100 million of thiol volatiles at ambienttemperature and pressure over 50 seconds in an oxygen environment. Insome cases, the cured material produces less than 1 part per 10 billionof thiol volatiles at ambient temperature and pressure over 50 secondsin an oxygen environment. In some cases, the cured material producesless than 1 part per 1 billion of thiol volatiles at ambient temperatureand pressure over 50 seconds in an oxygen environment. In someembodiments, the cured material produces less than 1 part per 10 billionof thiol volatiles at ambient temperature and pressure over 50 secondsin an oxygen environment.

The at least one monomer and/or oligomer and the thiol used for additivemanufacturing may be any monomer and/or oligomer or thiol compound asdescribed for the resin of the disclosure. For example, the at least onemonomer and/or oligomer includes an alkene, an alkyne, an acrylate oracrylamide, methacrylate, epoxide, maleimide, and/or isocyanate.

In some cases, the thiol has a molecular weight greater than about 200or greater than about 500. In some embodiments, the thiol has amolecular weight greater than about 100 and contains moieties includinghydrogen bond acceptors and/or hydrogen bond donors, wherein saidmoieties undergo hydrogen bonding.

In some cases, the resin includes the thiol and the at least one monomerand/or oligomer in about a stoichiometric ratio. In other embodiments,the thiol is less than about 20% by weight of the resin, less than about10% by weight of the resin, or less than about 5% by weight of theresin.

In other cases, the thiol includes an ester-free thiol. In someembodiments, the thiol includes a hydrolytically stable thiol. In someembodiments, the thiol includes a tertiary thiol.

Another embodiment of the invention provides a photopolymerizable resinfor additive manufacturing, the resin comprising: a blocked isocyanate;less than about 5% of a thiol; at least about 50% of one or more acrylicmonomers; and less than about 45% of one or more acrylic-functionalizedoligomers, wherein the resin is configured to react by exposure to lightto form a cured material; wherein the resin has a viscosity at roomtemperature of less than 1,000 cP; wherein the components of the resincan be combined and stored in a single pot for at least 6 months at roomtemperature with no more than 2%, 5%, 10%, 25%, 50% or 100% increase inthe viscosity of the resin.

Another embodiment includes, a photopolymerizable resin for additivemanufacturing, the resin comprising: a blocked isocyanate; less thanabout 5% of a stabilized thiol; at least 50% of one or more acrylicmonomers; and less than about 45% of one or more acrylic-functionalizedoligomers, wherein the resin is configured to react by exposure to lightto form a cured material; wherein the components of the resin can becombined and stored in a single pot for at least 6 months at roomtemperature with no more than with no more than 2%, 5%, 10%, 25%, 50% or100% increase in the viscosity of the resin. In some cases, the resin isconfigured to form a cured material in an aerobic environment.

Another embodiment of the invention includes a photopolymerizable resinfor additive manufacturing comprising: a blocked isocyanates; less thanabout 5% of a stabilized thiol; and at least about 50% of one or moremonomers; wherein the resin is configured to react by exposure to lightto form a cured material, wherein a layer of the resin about 100 μmthick is configured to form a cured material in no more than 30 seconds;wherein the cured material has a toughness in the range about 3-100MJ/m³ and a strain at break in the range about 30-1000%.

Additive Manufacturing of Resins

A photopolymerizable resin for additive manufacturing can be prepared inaccordance with the following procedure.

Resins can be printed in a Top-Down, DLP printer (such as the OctaveLight R1), in open atmosphere and ambient conditions. The printing vatmay be loaded with Z-fluid (usually, 70-95% of the total volume), andthen printing resin is put atop the Z-fluid (in commensurate levels;i.e. 5-30%). Printing parameters are input into the controllingsoftware: exposure time (which usually ranges from 0.1-20 seconds),layer height (which usually ranges from 10-300 micrometers), and thesurface is recoated between each layer in 0.25-10 seconds. Acomputer-aided design (“CAD”) file is loaded into the software, orientedand supported as necessary, and the print is initiated. The print cycleis: the build-table descends to allow the resin to coat the surface,ascends to a layer-height (also called the Z-axis resolution) below theresin surface, the recoater blade smoothes the surface of the resin, andthe optical engine exposes a mask (cross-sectional image of the printedpart, at the current height) causing the liquid resin to gel. Theprocess repeats, layer by layer, until the article is finished printing.In some embodiments, the 3D printed resin parts are post-processed bycuring at a temperature between 0-100° C. for between 0 to 5 hours underUV irradiation of 350-400 nm.

Material Characterization Techniques

The photopolymerizable resins for additive manufacturing can becharacterized by use of the following techniques.

Tensile Testing

Uniaxial tensile testing is performed on a Lloyd instruments LR5K PlusUniversal Testing Machine with a Laserscan 200 laser extensometer. Testspecimens of cured material are prepared, with dimensions in accordancewith ASTM standard D638 Type V. The test specimen is placed in the gripsof the testing machine. The distance between the ends of the grippingsurfaces is recorded. After setting the speed of testing at the properrate, the machine is started. The load-extension cure of the specimen isrecorded. The load and extension at the moment of rupture is recorded.Testing and measurements are performed in accordance with ASTM D638guidelines.

Toughness

Toughness is measured using an ASTM D638 standard tensile test asdescribed above. The dimensions of the Type V dogbone specimen may be asfollows:

-   -   Width of narrow section (W)=3.18±0.03 mm;    -   Length of narrow section (L)=9.53±0.08 mm;    -   Gage length (G)=7.62±0.02 mm;    -   Radius of fillet (R)=12.7±0.08 mm        Tensile testing may be performed using a speed of testing of 100        mm/min. For each test, the energy required to break can be        determined from the area under the load trace up to the point at        which rupture occurred (denoted by sudden load drop). This        energy is then calculated to obtain the toughness (MJ/m³)

Strain at Break

Strain at break can be measured using an ASTM D638 standard tensile testas described above. The dimensions of the Type V dogbone specimen may beas follows:

-   -   Width of narrow section (W)=3.18±0.03 mm;    -   Length of narrow section (L)=9.53±0.08 mm;    -   Gage length (G)=7.62±0.02 mm;    -   Radius of fillet (R)=12.7±0.08 mm

Tensile testing may be performed using a speed of testing of 100 mm/min.For each test, the extension at the point of rupture is divided by theoriginal grip separation (i.e. the distance between the ends of thegripping surfaces) and multiplied by 100.

Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) measurements can be performed ona Mettler Toledo DSC-1. A test specimen of 3-10 mg of cured material isplaced in the sample holder. Testing is conducted in a 40 ml/minnitrogen purge gas atmosphere at a temperature variation of 10°0 C./minfor three heat-cool cycles. Glass Transition Temperature (Tg) may bemeasured via a straight line approximation of the mid-point between theon-set and off-set of the glass transition slopes. DSC testing isperformed in accordance with ASTM E1356 Guidelines.

Dynamic Mechanical Analysis (DMA)

Dynamic Mechanical Analysis (DMA) measurements are performed on aMettler Toledo DMA-861. A test specimen of cured material 12 mm long, 3mm wide, and 0.025-1.0 mm thick is used. The specimen is subjected to atensile force at 1 Hz with a maximum amplitude of 10 N and a maximumdisplacement of 15 μm. Glass Transition Temperature (Tg) is measured asthe peak of Tan Delta (the ratio of the loss and storage moduli). DMAtesting is performed in accordance with ASTM D4065 guidelines.

Cure Rate

A sample of a given resin (approx. 1 g-10 g) is placed into a container.The container is placed below an optical engine, so that the resin isdirectly in the center of the projection area. A sample image (e.g. a 1cm×1 cm square) is projected onto the resin for a given amount of time(usually 0.1-20 seconds). The amount of time for an initial exposure isdetermined. The surface of the resin sample is inspected to determine ifa gel has formed. If a manipulable gel with fixed geometry (viz. asquare) has not formed, a new sample is generated with increasedexposure time, and the test is repeated until a gel is successfullyformed from a single exposure to approximate of the gelation point. TheDepth of Cure (DOC) recorded is the exposure time required for gelation.

Hardness

Hardness is obtained using a Shore A Durometer (1-100 HA±0.5 HA) inaccordance with ASTM D2240 guidelines.

Viscosity

Viscosity (mPa·s) may be obtained using a Brookfield LV-1 viscometer inaccordance with ASTM D2196 guidelines.

1. A photopolymerizable resin for additive manufacturing, the resincomprising: a blocked isocyanate; at least one monomer or oligomer; anda multifunctional nucleophile.
 2. (canceled)
 3. The photopolymerizableresin according to claim 0, wherein the at least one monomer or oligomerincludes an acrylic monomer, a thiol monomer or an -ene monomer.
 4. Thephotopolymerizable resin according to claim 0, wherein themultifunctional nucleophile includes at least one of a multifunctionalalcohol, a multifunctional thiol, or a multifunctional amine.
 5. Thephotopolymerizable resin according to claim 0, wherein themultifunctional nucleophile includes a multifunctional thiol.
 6. Thephotopolymerizable resin according to claim 0, wherein themultifunctional thiol has a molecular weight greater than about 100Daltons.
 7. The photopolymerizable resin according to claim 0, whereinthe resin includes about 1-20% of a multifunctional thiol.
 8. Thephotopolymerizable resin according to claim 0, wherein themultifunctional thiol includes a difunctional thiol.
 9. Thephotopolymerizable resin according to claim 0, wherein themultifunctional thiol includes a secondary thiol.
 10. (canceled)
 11. Thephotopolymerizable resin according to claim 0, wherein the secondarythiol includes at least one of Pentaerythritol tetrakis(3-mercaptobutylate); 1,4-bis (3-mercaptobutylyloxy) butane; or1,3,5-Tris(3-melcaptobutyloxethyl)-1,3,5-triazine. 12-14. (Canceled) 15.The photopolymerizable resin according to claim 0, wherein the at leastone monomer or oligomer includes an acrylic monomer. 16-17. (Canceled)18. The photopolymerizable resin according to claim 0, wherein the resinincludes 1-70% of a blocked isocyanate.
 19. The photopolymerizable resinaccording to claim 0, wherein the blocked isocyanate includes at leastone of a uretdione, a biuret, an allophanate, an isocyanaurate,methylene dicyclohexyl diisocyanate (MDI) or toluene diisocyanate (TDI).20. The photopolymerizable resin according to claim 0, wherein theuretdione is a uretdione of hexamethylene diisocyanate (HDI), auretdione of isophorone diisocyanate (IDI), a uretdione of methylenedicyclohexyl diisocyanate (MDI), a uretdione of hydrogenated methylenedicyclohexyl diisocyanate (HMDI), or a uretdione of toluene diisocyanate(TDI).
 21. The photopolymerizable resin according to claim 0, whereinthe isocyanaurate is an isocyanaurate of hexamethylene diisocyanate(HDI), an isocyanaurate of isophorone diisocyanate (IDI), anisocyanaurate of methylene dicyclohexyl diisocyanate (MDI), anisocyanaurate of hydrogenated methylene dicyclohexyl diisocyanate(HMDI), or an isocyanaurate of toluene diisocyanate (TDI).
 22. Thephotopolymerizable resin according to claim 0, wherein the biuret is abiuret of hexamethylene diisocyanate (HDI), a biuret of isophoronediisocyanate (IDI), a biuret of methylene dicyclohexyl diisocyanate(MDI), a biuret of hydrogenated methylene dicyclohexyl diisocyanate(HMDI), or a biuret of toluene diisocyanate (TDI).
 23. (canceled) 24.The photopolymerizable resin according to claim 0, wherein the blockedisocyanate includes an isocyanate and a blocking agent. 25-26.(Canceled)
 27. The photopolymerizable resin according to claim 0,wherein the blocking agent includes at least one of a nucleophile,derivatives of alcohols, hindered amines, caprolactams, phenols, oximes,or pyrazoles malonates.
 28. (canceled)
 29. The photopolymerizable resinaccording to claim 1, wherein the resin is configured to react byexposure to light to form a cured material, wherein the cured materialhas a strain capacity of between about 10% and about 500%. 30.(canceled)
 31. The photopolymerizable resin according to claim 1,wherein the resin is configured to react by exposure to light to form acured material, wherein the cured material is post-treated with heat.32-351. (canceled)
 352. The photopolymerizable resin according to claim15, wherein the resin includes 30-90% of an acrylic monomer.